This is an attempt to cover some basics of the modern AVR (Audio/Video receiver). This type of receiver is also known as a home theater receiver. The modern AVR should include at minimum –
* Video switching
* Analog and digital audio switching
* Five channels of amplification (or more)
* Standard audio decoders (e.g. Dolby Digital)

(updated in 2014)

These features seem to be standard even on the cheapest models-

* HDMI (there are differences in HDMI - check AVR specs for details)

* Surround sound from stereo sources (e.g. Dolby Pro Logic II)

Many models now support a wide variety of digital audio options in conjunction with network connectivity. An AM/FM tuner is usually present, but in the digital age, that could change in the future.

What's an AVR?

An audio/video receiver.

They provide switching for multiple audio-video devices, amplification for a surround sound setup, an AM/FM tuner and video switching capabilities.

An AVR paired up with decent speakers should give you much better sound than your TV speakers, and is highly recommended.

Output power is certainly of some importance. The problem is with AVR power ratings. Their output power is not measured consistently. For that reason, you may be trying to compare apples and oranges when trying to compare the output power of two different AVRs.

Impedance is a measure of electrical resistance. Rated impedance is usually 8 ohms for AVRs. AVRs may also show a 6 ohm rating. Most AVRs are not rated for 4 ohms. If you choose to use 4 ohm speakers with an AVR not rated for 4 ohm speakers, you may run into problems. Excess current which results from lower impedance loads could damage a receiver which is why they have protection circuits. Some people have used 4 ohm speakers with AVRs not specifically rated for it. Whether or not you can get away with this depends on factors such as how loud you want your sound, what speakers you have and the receiver design. Prudence in operating a receiver that's not rated for 4 ohm speakers is dictated.

Note that a nominal impedance is listed for speakers. Their actual impedance will vary over frequency. And 8 ohm speaker might have an impedance of 20 ohms in one section of it's response curve and 4 ohms in another. Some people worry that these variations in impedance can make some speakers difficult for a receiver to drive. It's not clear (to me) how legitimate a concern this is though.

AVRs can be measured using different signals. You will typically see either a 1 khz signal used or a full bandwidth (20 hz to 20 khz) used in the receiver's specs. A 1 khz signal will result in a higher rated power than a full bandwidth signal, and manufacturers will use that to get a higher rated power.

Total Harmonic Distortion is the common distortion measurement used in AVR power output ratings. It's a measure of how much the output signal deviates from the input signal. It might be shown as THD, or THD+N (THD plus noise.) Don't obsess too much about THD, but there's some things it can tell you. If you see a receiver who's power is rated with a high THD, it's probably being spec'd past it's clipping zone. In other words, you would not want to operate it at that output level. High THD is relative, but a measured THD + N of over %0.1 could be a bit misleading. Power output continues to increase past the point of clipping, but so does distortion.

Below clipping, any competent receiver should have fairly low THD. Is it worth thinking much about THD when buying a receiver? Not too much, as there's a lack of information on exactly at what point distortion becomes audible.

AVRs are often not measured with all channels driven simultaneously. This is allowed in the US by FTC rules. Most 100x7 watt AVRs aren’t going to put out 700 watts continuously with all channels driven. The amplifiers in AVR usually share a single power supply. Each amplifier channel is capable of putting out 100 watts, but the power supply can’t simultaneously supply enough power for all of them to put out 100 watts at the same time.

A 100x7 watt AVR measured may put out less than 50 watts per channel with all channels driven. Some AVRs, such as those from Harmon Kardon, are measured with all channels driven. When compared to an AVR in the same price range, they will have lower power.

As mentioned above a number of times, exceeding the amplifier’s power output limits will likely result in clipping. Clipping can damage speakers. See the section on clipping for more information.

Salespeople will sometimes mention that a given model or brand has a high current design. The idea is that the receiver’s power supply can produce more than “average” current. So when you connect speakers with an impedance lower than 8 ohms, the receiver will be up to the task. Also, as speakers have a variable impedance, some will claim these high current receivers will work better than a non high current receiver with any speakers. Without specific measurements, I fail to see how saying a receiver has a high current design has much meaning.

Should you favor AVRs measured with all channels driven? Not necessarily. They will likely be rated lower than a comparably priced AVR which is not ACD rated. For example, Harmon Kardon receivers are measured with all channels driven, and their per channel power is lower than comparably priced receivers for this reason.

The fact is, the power measurements given by the manufacturers don't give enough information for direct comparisons. It's one thing to rate a receiver with two channels driven into an 8 ohm dummy load. It's another thing to try to understand how much real world power you will have once you hook up speakers to the receiver and playback a movie.

Power by itself does not tell the whole story. Speakers differ in how sensitive they are. Speaker sensitivity is measured as a given Sound Pressure Level (SPL). SPL is measured using the decibel (http://en.wikipedia.org/wiki/Decibel) scale. Because of the way humans hear, a doubling of amplifier output power results in a change in SPL of 3dB (decibels.) The decibel scale is used because it’s logarithmic like human hearing. According to most sources, a change of 10dB is perceived as roughly twice as loud, and a change of 3 dB is roughly the lowest change in SPL which is noticeable by human hearing.

Speaker sensitivity is measured by the SPL measured from one watt away from the speaker, with one watt of input. A brief chart should help indicate the difference between amplifier output power, SPL and speaker sensitivity. Speaker sensitivity is a measure of how much SPL is produced by a speaker with one watt of input power at one meter away.

You should notice that it takes very little power to hit 90 dB. We will hear 91 dB from four watts of input into an 85 dB speaker and 90 dB with with one watt of input to a 90 dB speaker. Obviously sensitive speakers make a difference.

Power needs increase very fast. We need 128 watts for 111 dB, and only 64 watts for 108 dB (with 90 dB speakers.)

Distance plays a factor. A distance of 12 ft will reduce SPL output by approx 12 dB (sound decreases by approximately 6 dB for each doubling of distance.) To hit an 85 dB SPL average listening level from 12 ft away with 90 dB (sensitive) speakers, you will only need approx. 4 watts of power! Not as much as you may have thought.

The chart should also show you why a 120x7 watt AVR may not be louder than a 100x7 watt AVR. 100 watts gets you 110 dB SPL, where 120 gets you 111 dB SPL.

As mentioned above, one way to take some burden off your amp is to use a powered subwoofer. Another is using efficient speakers. Finally, you can consider a separate power amp. See the section below on using external amplifiers.

What is clipping?

Clipping is the undesirable result of trying to amplify the input signal beyond an amplifier’s limits. As you turn up the volume, you come closer to the amplifiers maximum output voltage.

The power supply of an amplifier provides a maximum voltage that the amplifier’s transistors can amplify the input signal up to. The power supply has two voltage rails providing a positive and negative voltage of the same value. For example, the power supply may have a +35 volt and -35 volt voltage rail. If the amplifier’s transistors try to amplify the input signal past these limits, they will not be able to. The part of the signal exceeding these limits will be clipped at the limits (see the photo on this page - http://en.wikipedia.org/wiki/Clipping_(audio))

Drawing too much current from an amplifier could also result in clipping as the power supply voltage may drop. One possible scenario is trying to drive a speaker or speakers with too low of an impedance. This is a bad idea in any case. Ideally you would simply trip the amplifier’s protection circuits. But you could damage the amplifier.

Clipping can damage speakers. Clipped signals have more average power. Speakers are inefficient and convert much of the power sent to them into heat. As the average power of the signal increases, the speaker’s ability to dissipate heat may be exceeded.

An often repeated phrase is that too little power destroys speakers. What people mean is that insufficient power makes it more likely you will turn up the volume to the point of clipping. Amplifier makers will often recommend you buy more power than you need to avoid clipping. Too much power can destroy speakers, but that seems to be uncommon. It seems prudent though, not to drive speakers rated for 50 watts with 200 watts of power.

What do the numbers mean on volume displays (when volume is show in dB) ?

Many AVRs show volume in dB rather than a scale such as 0 to 100. Some people wonder why this is, especially why number go negative.

dB is short for decibel. A decibel measures the difference between a quantity and a reference value. Unlike a unit like volts or watts, dB has no direct physical meaning. It's dependent on what quantities are measured.

There are different kinds of dB. For example, sound pressure (SPL) is also measured in dB. There is a correlation between SPL and your volume readout due to the fact that they both use dB. And I will explain that in a moment.

Before we go further, the reason volume is often negative is due to how logarithms work. As the formula for dB uses logarithms, a value less than reference will be negative. When our current volume is less than the reference volume, it will be negative.

As different receivers can use different values for their reference volume, let's choose one for discussion purposes. THX came up with a concept called THX reference level. A receiver calibrated to THX reference level will play back movies at an average of 85 dB SPL when their volume is set to 0 dB. For this discussion, we will assume this is how all receivers work (they don't, just to be clear.)

Any volume which produces an SPL less than this average level of 85 dB, will be negative, because that's the way dB works as mentioned above. A volume 0 dB would produce an SPL of 85 dB. A volume over 0 dB will be greater than the reference volume.

Because 0 dB volume on our receiver puts out 85 dB SPL, we expect -10 dB on our receiver to put out 75 dB. This works on my receiver, anyway, and hopefully works on most receivers. For a volume of -20 dB, we would expect an SPL of 65 dB.

An SPL increase of 10 dB is approximately twice as loud to human hearing. An SPL decrease of 10 dB would be half as loud. A 3 dB change is just noticeable. Some people may be able to hear smaller changes.

I want to know about using external amplifiers with my AVR?

Some receivers allow for connecting external amplifiers. These receivers provide pre-out jacks to connect some or all of a receiver’s channels up to an external amplifier.

Before buying external amplification, the first consideration should be whether or not you need them. Why spend money you don’t have to?

One indication of needing more power is trying to turn up your volume to the point where the sound gets noticeably harsher. This is easy to do with music, in my experience.

With movies, it’s a bit harder to assess power needs. As I am sure you have noticed, movies have a wide dynamic range. You may turn up the volume to hear a quiet dialog scene only to be assaulted with loud sounds in the next scene. Hence, the need for more power occurs during peaks in movies. Scenes with explosions may create peaks over 10 dB higher than your average listening level. While some music may contain peaks of this magnitude, it’s more common for music to be less dynamic than movies.

To gain some understanding of system power level, I will describe a brief scenario. In our scenario, I will try to assess peak power levels achievable. Of course we want to know the maximum SPL possible without clipping (see the section on clipping.)

In this scenario, let’s assume a 7.1 speaker setup. We have a powered subwoofer, and seven speakers powered by our receiver. Many receivers cannot put out rated power when all channels are driven. I will pick out one measurement I have seen, and choose 50 watts / channel for purposes of this discussion. Let’s assume our speakers have a sensitivity of 90 dB. That means that the speaker will output 90 dB SPL from one meter away. With these numbers, and I will omit the math, we will have a peak SPL per speaker of about 107 dB.

Read the section above on power if you don’t understand SPL. As mentioned in that section, we will lose 6 dB for each doubling of distance. We will assume an average loss per speaker of 10 dB (indicating an average distance of 10 ft from our speakers, I will omit the math.)

Another fact to know is how much dB we gain from multiple speakers. This is a non trivial calculation, so I will simplify it. In my own tests, my total peak in SPL on one movie scene was 3 dB more than the highest per channel peak. So I will use that number.

Given all of the above information, we can approximate peak SPL allowed by our receiver. 107 dB peak per speaker minus 10 dB loss for distance plus 3 dB gain for gain from multiple speakers. That gives us 100 dB peaks. If the peaks are 15 dB over our average listening level, that would give us 85 dB average.

I suggest buying an affordable SPL meter and doing your own measurements and evaluation.

The main purpose of more amplification is to avoid clipping at your desired listening level. Harshness or obvious distortion indicates the need for more power.

If you have decided that you need more power, adding amplifiers is one option. You will need an AVR with pre-outs. These are line level outputs for each channel. A receiver could have between 6 and 8 pre-outs, one per channel.

A good question is how many channels to externally amplify? The author of this FAQ did some very limited testing to determine per channel power usage. The test scene was the first scene in the movie Sahara. If this scene is typical, the sub needs the most power. It peaked about 3 dB higher than the left, center and right channels. This is a good argument for using a powered subwoofer. The left, center and right channels needed the next most power. The center actually peaked a bit higher than the left and right channels. The surrounds were at least 3 dB lower indicating that they required about one half the power as the main channels.

There are two main amplifier markets. Pro audio and home audio. The difference in power per dollar can be great. Pro audio amplifiers are typically more affordable.

The most obvious downside of pro audio amps is that most have a fan. This is good for the amp, but may be annoying for home theater use. Some adventurous souls have removed or modified the amp fans. Some people feel pro amplifiers are designed for quantity, not quality. This is one of those endless debates in audio. You will have to decide this debate for yourself.

There are a few different types of connectors. Home audio amplifiers will have RCA inputs which allow for the use of common RCA cables.

Some amplifiers may have balanced (XLR) inputs (http://en.wikipedia.org/wiki/XLR). Some (usually expensive) receivers will have XLR outputs which can be connected to the XLR inputs on an amplifier.

Many pro amps will not have RCA inputs. The best connection to use with them is a 1/4” mono plug. These plugs have only two conductors. You will need to buy a cable with RCA cables on one end and 1/4” mono plugs on the other end.

Amplifiers may come with level controls (also called gain controls). The level control may help match the amplifier with your receiver. They are simply attenuators which control the signal gain. Start with the level control half-way and increase it until it’s approximately the correct volume. A good way to do this is to measure the SPL before connecting the external amp. Then, using the same volume level and source material (such as a song), match the same SPL using the level controls if possible.

You need to make sure all speakers are properly balanced using an SPL meter or the receiver’s auto setup.

Amplifiers have a lot of different specifications. I personally don’t worry too much about them. One specification of interest is called input sensitivity or gain. Input sensitivity is a measure of how strong a signal is required to drive an amp to it’s full (unclipped) power. Receivers may not have enough power to do this. My own setup has a Yamaha RX-V2700 and a Mackie FR-800. The Yamaha RX-V2700 puts out 1v from it’s pre out jack. The Mackie FR-800 amplifier has an input sensitivity of 1.15 volts. The RX-V2700 has insufficient power to drive the Mackie to full power. I don’t see this particular situation as critical as I don’t need the Mackie’s full power.

Input sensitivity may also be listed as gain in dB. Engineers seem to like to use different measurements to describe the same thing. One 200 watt amp I saw, for example, listed it’s gain as 32 dB. What does that mean? It means that the amplifier can amplify the input signal 39.8 times. On this amp this is equivalent to an input sensitivity of approx 1 volt*.

* The math on this is a bit more than most people would want to look at. Feel free to ignore these calculations. These are my own calculations, and they could be wrong. And there could be easier ways to come up with this answer.

The formula to calculate voltage gain from dB gain is –
10 ^ ( gain / 20) – 10 to the power of gain (in dB) times 20; this is the inverse of the common dB formula. We get a voltage gain of 39.8. That is, this amplifier can amplify voltage by a factor of almost 40.

We need a formula to calculate voltage from power and resistance –
v = sqrt( p * r) – Voltage is the square root of power times resistance

We want to drive a 200 watt amp to it’s max power into an 8 ohm speaker. The voltage needed is sqrt ( 200 * 8) or 40. The voltage gain expressed by 32 dB is approximately 40v. An input of 1 volt can be amplified to approximately 40. Which means an inputs of 1 volt can drive the amplifier to full power. Which gives us an input sensitivity of 1v.

How about sound quality?

Buyers often want to know whether one AVR sounds better than another. This is a perfectly reasonable question. Unfortunately, it’s difficult to answer.

Ideally, an AVR would amplify an input signal without adding any distortion. In reality, all AVRs will add distortion. AVRs do more that amplify input signals. They have all sorts of digital audio processing, some of which could

Also, AVRs do way more than amplify signals. They also can decode digital audio, process analog surround sound, perform bass management and apply room correction algorithms.

Whether AVRs actually sound appreciably different than each other is endlessly debated in online forums. A number of well known blind listening tests have been done, and listeners were not able to reliably differentiate one amplifier from another. These tests are not proving amplifiers sound identical. Instead, they demonstrate that amplifiers sound enough alike that people cannot reliably tell them apart. A person named Richard Clark has offered money to anyone who can distinguish one amplifier from another (http://www.tom-morrow-land.com/tests/ampchall/index.htm).

An article by Rodd Elliott describes measurable factors which can an amplifier’s sound quality ( http://sound.westhost.com/amp-sound.htm.) Specifications are just one factor when buying AVRs. Obsessing over specs is not recommended.

Power is very important to sound quality. If your AVR does not have enough power for your needs, you will likely try to turn up the volume to the point of distortion. In my experience, it’s especially important to have sufficient power when listening to music.

Speakers and room acoustics are arguably more important to sound quality than the AVR. Speakers have high distortion (as much as 10%) and their frequency response not as flat as an AVRs. Rooms affect sound in a number of ways, and few people are willing to apply room treatments in an attempt to compensate.

One way to assess AVR sound quality is to read a review. Reviews can be useful, but you are relying on the perception of the reviewer. Also his equipment and listening room are different than yours.

Another way to assess AVR sound quality is in a store’s listening room. There are limitations to this method due to the large number of variables. Listening tests need to set both AVRs such that they are playing at the same volume (ideally using a sound meter.) AVRs have auto setup options which could be a factor. Are the tone controls flat? And of course the speakers and room likely don’t match your setup.

Another method of assessing AVR sound quality is owner feedback. Owner feedback is most useful for pointing out day to day issues. As mentioned a number of times, sound is subjective; keep this in mind when reading owner feedback. And of course they likely have a different setup than you do.

Sound quality is clearly important. If getting an objective indication of sound quality is difficult, how does a buyer assess sound quality? One suggestion is to stick to manufacturers with good owner feedback. Reading feedback in online forums should give you a good idea which brands are most trusted. Buy from a source with a liberal return policy in case the AVR does not meet your needs. Make sure you buy an AVR with sufficient power

What do the numbers 5.1/6.1/7.1 mean?

A 5.1 AVR has five amplifiers.

A 6.1 AVR has six amplifiers, the additional amplifier is for an optional rear surround speaker, see the sections on Dolby EX and Dolby Pro Logic IIx for more explanation.

A 7.1 AVR has seven amplifiers the additional amplifiers are for two optional rear surround speakers, see the sections on Dolby EX and Dolby Pro Logic IIx for more explanation.

The .1 indicates that the AVR handles the Low Frequency Effects channel present on movie soundtracks. AVRs don’t have amplifiers for the LFE channel (no AVR I know of anyway.) They have an output connector for hooking up a powered subwoofer.

AVRs offer various bass management modes. Owners can set the AVR to output low frequencies (all low frequencies, not just the LFE) to the main speakers if they don’t have a powered subwoofer. Or if they have a subwoofer, they can send all low frequencies to it. A powered subwoofer reduces the load on the AVRs amplifier section. There’s usually a setting for which frequencies are handled by the powered subwoofer. This is called the crossover setting. A typical value is 80hz which indicates that frequencies below 80hz will be sent to the sub.

What are Dolby Digital and DTS?

Back in the mid 70s, Dolby developed a method of adding surround sound to 35mm films, with it first being used on Logan's Run. Since then many different surround sound technologies have been created.

Perhaps the most successful format of all time is Dolby Digital which is present on almost every DVD soundtrack. To take advantage of Dolby Digital you need to hookup your player to your AVR with a digital cable, or a set of multi-channel analog cables. And you need at least four speakers (one each for the left, right, left-surround and right-surround channel.) A common setup is six speakers (left/center/right/left-surround/right-surround/powered subwoofer.) AVRs can send the center channel to the left/right channels if desired and can send the LFE channel to the left/right channels as well if you prefer fewer speakers in your setup.

Besides Dolby Digital, DTS is also relatively common. DTS has a higher bandwidth signal, but that does not mean it's guaranteed to sound better. They both compress the original signal using methods which try to remove parts of the audio signal a human cannot hear. Dolby Digital is considered to use a more efficient method of compression which partially explains there difference in bandwidth. The bottom line is both are impressive achievements and were a large step up from soundtracks available to the consumer on VHS tapes.

Dolby Digital and DTS are often referred to as codecs (coder-decoder.)

What are Dolby Digital EX and DTS ES?

Some DVD soundtracks have 6.1 rather than 5.1 soundtracks. 6.1 soundtracks contain a rear surround channel. AVRs with 6.1 capability or 7.1 capability have Dolby and DTS decoders for these soundtracks along with additional amp(s). In most cases, the AVR can automatically detect the proper decoder to use. To take advantage of these, one or two speakers are needed to play back the rear surround channel.

Using a 6.1 or 7.1 speaker setup is optional; you can play 6.1 DVD soundtracks back in 5.1. Also, 6.1 DVD soundtracks are uncommon.

What are Dolby Pro Logic, Dolby Pro Logic II and Dolby Pro Logic IIx?

Dolby Pro Logic was a surround format commonly used on VHS tapes. Dolby Pro Logic II was a follow up decoder from Dolby Labs. It worked with any two channel material unlike Dolby Pro Logic which only worked with Dolby encoded soundtracks.

The latest Dolby decoder in this series is Dolby Pro Logic IIx. This decoder works with any source. It also works with 7.1 speaker setups. It can expand any two channel source to a 5.1, 6.1 or 7.1 soundfield. It can expand a 5.1 source to a 6.1 or 7.1 soundfield as well.

It’s also possible to use Dolby Pro Logic IIx for when playing movies with a Dolby Digital EX soundtrack. Some very well informed people claim it’s preferable to use Dolby Pro Logic IIx movie mode when playing Dolby Digital EX movies.

In summary, Dolby Pro Logic IIx can be use for playing movies with either 5.1 or 6.1 soundtracks. The one possible exception is 6.1 DTS ES movies. But some receivers will let you apply Dolby Pro Logic IIx processing to 6.1 DTS ES movies as well.

What about modes like Action, Game, 7-channel stereo modes (etc.) ?

AVRs usually contain some sort of artificial surround sound generation modes. Some people like them some people don’t.

Movie modes work on top of your typical decoders like Dolby Digital. They will add reverb to give you the feeling you are in a theater.

Five and seven stereo mode while hated by some, are at very least, great for parties. The overall volume needed to cover a room can be lower - or you can just crank it up if you didn’t really want to talk to the people you invited.

Some AVRs include enchanced modes that are supposed to improve the playback of MP3 sources. They supposedly attempt to restore audio information lost from the compression process.

Many feel that some of these modes subtract rather than adding to your listening enjoyment, but only you can make that decision for yourself.

What is lossless vs. lossy compression?

Compression is a method to reduce the size of data. A common compression method is used by computer ZIP files. Compression takes advantage of data redundancy. Consider a restaurant menu with numbered items. You could write an order for the kitchen using only the numbers as long as everyone knows what the numbers mean.

Computer ZIP files use lossless compression because data loss is usually unacceptable. The size of the file is reduced with no loss of data. Audio data is less critical, and contains data that can’t be heard due to human hearing limitations (http://en.wikipedia.org/wiki/Auditory_masking.) A common lossy compression method for audio is MP3. Audio quality of MP3s can be improved by using less compression. The compression rate of an MP3 file is usually specified as a bitrate. Higher bitrates indicate to the MP3 decoder to keep more data. in general, MP3 files with a higher bitrate will be closer to the original audio file. Given a high enough bitrate, an MP3 file should be indistinguishable from the original.

Lossless compression is theoretically better than lossy compression. DVDs didn’t have enough room to store soundtracks without using lossy compression. Even though DVDs use lossy compression, they usually sound very good.

One way to get a rough idea of lossless compression is to play around with a CD ripping program. Rip at high and low rates, and compare the resulting MP3s. For example, rip the same track at both 256kbs and 64kbs and compare those MP3 files. At some point you may not be able to hear a difference between two files with high bitrates such as 256 kbs and 320 kbs.

Audio compression methods such as MP3 and Dolby Digital are commonly called codecs (coder-decoder.)

What do the terms bitstream, PCM and MPCM mean ?

They all refer to different ways of sending audio data over a digital connection.

PCM (Pulse Code Modulation) is a ubiquitous way of representing audio data. Two common uses of PCM are on CDs and in computer WAV files. The original audio is sampled at fixed intervals and a numbers (samples) are generated that represent the original the audio signal. The number of samples per second is called the sample rate. CDs use a sample rate of 44.1khz or 44,100 samples per second. The size of the number used to store the sample is called the bit depth. CDs use a 16 bit number which can store a value between 0 and 65535. The larger the sample rate and bit depth, the closer the digital version approximates the original analog signal.

Bitstream audio refers to non PCM audio streams. The term usually refers to audio that was compressed using some codec (coder-decoder.) The term is often used for an audio stream sent as it was stored (such as on an optical disc.) Sometimes audio is recoded to a different codec. See below for an example of this.

The first common digital connection was S/PDIF (Sony/Philips Digitial Interconnection Format.) S/PDIF allows for the transmission of either two channel (stereo) PCM or a Dolby Digital or DTS bitstream.

HDMI expands on S/PDIF by allowing more than two channels of PCM. PCM with more than two channels is often called Multi Channel PCM or MPCM. HDMI supports the transmission of more types of codecs (compression methods) than S/PDIF. HDMI allows Dolby Digital, Dolby Digital+, DSD (SACD), DTS, DTS-HD Master Audio, and TrueHD to be transmitted as bitstreams.

Some high definition players can’t output Dolby Digital+, DTS-HD Master Audio or TrueHD bitstream. For the rest of this section they will be referred to as HBR (High Bit Rate) codecs.

For example, you may have an AVR with a TrueHD decoder, and a player that can’t output HBR codecs as a bitstream. Even if you hookup the player to the AVR with an HDMI cable, you will never see the TrueHD indicator light up on the AVR. The audio will be dependent on your exact setup. If you have an AVR that supports MPCM over HDMI and set the player properly, the player will decode the audio track and send MPCM over HDMI. The sound quality should be identical to decoding the audio track at the player. The audio could also be downcoded to Dolby Digital or DTS. The audio should still sound great, but HDMI/MPCM is preferable. There have been firmware updates for some players to allow them to output HBR codecs as a bitstream.

Many high definition players can’t decode DTS-HD Master Audio. If your player can’t send DTS-HD MA bitstream or your AVR can’t decode it, your player should be able to still play the DTS-HD soundtrack, but only the lossy, DTS core.

There is a limitation when using bitstream with HD-DVD and Blu-ray players. Players cannot output secondary audio (or interactive audio from menus) when bitstream audio output from the player is enabled. That’s because secondary audio requires decoding the audio track and then mixing the secondary audio at the player. To output it as bitstream would require recoding the audio (which isn’t technically impossible, but it’s a non trivial task.)

Some people feel bitstream is a better method of transmitting audio, because it’s less subject to timing errors (called jitter.) The AVR has to buffer up the data to decode it, which helps reduce jitter.

Is lossless audio worth upgrading for?

This point is endlessly debated. In one article, the differences were not found to be dramatic. There’s no doubt that lossless can sound better than lossy. The biggest difference seems to be when comparing the relatively low rate Dolby Digital (448 kbs max) on a DVD to lossless audio.

Note that Blu-ray discs have higher rate Dolby Digital than you will find on a DVD. The max rate is 640 kbs. This means that Dolby Digital on a Blu-ray disc, can be closer to lossless. People have told me that discs with a TrueHD track should also have a Dolby Digital track for compatibility. I suspect that track will always be the higher rate of 640 kbs.

DTS-HD Master Audio contains a core DTS track plus the lossless extension. Most people should be able to use this core track, which is typically a very high 1.5 Mbs rate. Some evidence seems to suggest this is very close to lossless quality.

For movies, audio quality is arguably less critical than music. One could argue that the lossy audio available on Blu-ray discs is good enough for movies. Of course some people will always demand the best possible audio.

Some have said the difference with lossless is impressive. But people often seem to claim impressive differences when others don’t feel the difference is dramatic. Audio claims should always be critically evaluated due to the highly subjective nature of sound.

In conclusion, you should typically be able to hear very good audio quality from lossy tracks on Blu-ray. You may want to wait to upgrade your receiver for more reasons than just getting lossless. If you have the money, and prefer enjoy the best possible sound, by all means upgrade to a system which can decode and play lossless audio.

What do I need to enjoy lossless audio (Dolby TrueHD and DTS-HD Master Audio)?

To make this section shorter, it will refer to TrueHD and DTS-HD Master Audio as HBR (High Bit Rate) Audio. Dolby Digital+, and DTS-HD High Resolution are also grouped in this category, but they are not lossless. When this section uses the term codec, it refers to the algorithm used to encode the audio. Codec is short for coder-decoder.

See above for a refresher on PCM.

You need one of these three setups –
• A player than can decode HBR audio and send it via HDMI; An AVR that can accept multi-channel PCM (MPCM) over HDMI
• A player that can decode HBR audio with analog outputs; An AVR with multi-channel analog inputs
• A player that can output HBR audio as a bitstream over HDMI; An AVR with the appropriate HBR audio decoders

Bitstream audio, works just like a DVD player hooked up with S/PDIF (e.g. optical). MPCM works just like a CD player hooked up with S/PDIF. In the first scenario, encoded audio is sent to the receiver which decodes it to PCM. In the second scenario, the audio is already in PCM. PCM is just a series of numbers representing the signal.

There is no theoretical sound quality difference to decoding at the receiver vs. the player. The decoding process will produce identical PCM output. That’s not to say that there are no differences. From a decoding standpoint, there should be no difference if both decoders work correctly. Once the audio is decoded though, differences in transmission or processing could occur. Think of the situation like this. Does it matter if you send a computer ZIP file to a friend or if you send the unzipped file? In both cases the contents will be the same.

AVRs can have limitations when playing HDMI/MPCM audio that they don’t have with bitstream. One possible restriction is that the AVR cannot apply any surround processing to HDMI/MPCM such as Dolby Pro Logic IIx. Some people have run into bass management issues with HDMI/MPCM. One problem, reported by some users, was that their low frequency effects/bass channel was too low. The explanation for this was that the LFE channel is recoded 10 dB low. The expectation is that the receiver would boost this by 10 dB to give the LFE channel a higher dynamic range than the other channels. Some receivers apparently were not applying this 10 dB boost.

If you use bitstream audio over HDMI you won’t get secondary audio. This could change in the future. But it will require the player to decode the audio, mix the secondary audio and then re encode the audio.

It may not be obvious, but when using MPCM for TrueHD or DTS-HD Master Audio, those indicator lights on your AVR will not light up. The AVR has no clue what the original audio codec was.

Why are there so many connections on the back of my AVR?

Technology changes have produced an obscene number of connections. The most common are:

Analog Audio

* RCA terminated stereo connection
- This is a pair of RCA jacks usually color coded red (for the right channel) and white for the white channel.

* RCA terminated multi-channel audio connection
- This is a set of RCA plugs for a multi-channel audio connection as from a DVD player. One use for this would be from a player with an SACD or DVD Audio decoder.

Digital Audio

* Optical or COAX terminated S/PDIF connection
- This common digital connector comes in two flavors - optical or coax (RCA terminated.) While the merits of these connections have been debated, pratically speaking they perform the same job. This cable can be used for CD players, DVD players or high definition players to send stereo, Dolby Digital or DTS. It does not support the newer high defintion audio formats sush as TrueHD.

Analog Video

* RCA terminated composite video connection
- Usually color coded yellow this is used for analog composite video. It's commonly used to connect VHS players, DVD players, cam corders and game systems. It's the worst possible quality video connection as composite video suffers from some signal degredation due to combining the color and chrominance (color) and luminance (brightness) signals.

* RCA terminated component video
- Often color coded red, green and blue, component video carries two separate color difference signals and a luminence signal. Color coding may not be consistent. Make sure that the same physical cable connects Y to Y, Pb to Pb and Pr to Pr. This is the best analog video connection found on AVRs.

HDMI (Digital audio and video)
- See "What is HDMI?"

What is HDMI?

HDMI is a single cable connection for digital audio and video. Like most technologies it has advantages and disadvantages.

Disadvantages –
• Compatibility issues
• Connector is not as tightly fitting as some connectors
• If you prefer connecting audio to your receiver and video to your TV, you may have to buy an HDMI switch or splitter
• Other video connections may allow for longer cables to be, such as to a projector
• HDMI can suffer from various problems when the signal flow is interrupted; e.g. the TV being turned off, the channel change on a cable box, etc;

Compatibility may be the biggest problem with HDMI. People have had problems when connecting their cable boxes into their AVRs with HDMI. An oft cited culprit is HDCP, a copy protection mechanism built on top of HDMI. Your cable box may work fine when connected with HDMI to your TV, but refuse to work through your AVR. An update to the cable box’s firmware may solve this. A different model of cable box may also solve the problem, if available.

HDMI has three different common versions; 1.1, 1.2 and 1.3. 1.2 added support for SACD. 1.3 adds the ability to transmit high bit rate audio “bitstreams”. This allows for decoding to be done by the receiver, rather than an HD player. This is similar to how Dolby Digital and DTS are usually decoded.

HDMI supports both multi-channel PCM audio. The previous standard for connection for digital audio, S/PDIF, only supported two channels. In current implementations, HDMI can transmit up to 7.1 channels of PCM audio. PCM is uncompressed audio. HDMI can transmit very high quality of PCM audio; up to 192khz/24 bits (24 bits of resolution at up to 192,000 sample per second.)

HDMI has an advantage in this age of digital video. Cable is moving to the digital domain, and satellite was already there. Game consoles like the PS3 and Xbox 360 output digital video over HDMI. DVD players and Blu-ray players output digital video. Using an analog connection from these devices requires a digital to analog conversion. If your TV is an HDTV with an addressable display such as LCD, DLP or plasma, and most are, yet another conversion must be done. Avoiding these conversions can certainly improve the video signal.

Many HDMI features are optional. Not every HDMI AVR is made alike. Some AVRs may not handle 1080p as mentioned above. Some may only switch HDMI video, and not handle audio. Some receivers can apply processing to HDMI/PCM and some can’t. For example, you may not be able to apply Dolby Pro Logic IIx to HDMI/PCM for 7.1 audio from a 5.1 soundtrack. These are just some of the differences.

HDMI is a single cable solution for both audio/video. This is generally a good thing, but may make it more difficult to make certain hookups. For example, if you want to have a different audio and video connection from a device, you may need to get an HDMI splitter. One reason to have different connections is to take advantage of some TVs ability to set different video settings on each input. The ability to do this may be less important in the age of digital video.

What are technologies like YPAO, Audyssey and MCACC? (auto setup and room calibration technologies) ?

These technologies serve two purposes. One is to automatically level your speakers. They can also give you useful information about whether you have hooked up your speakers properly (when they work, that is.)

The other purpose is to setup the AVRs room correction settings. These are supposed to help compensate for uneven frequency response in rooms.

If you are not into making manual adjustments, it’s suggested you run the setup as specified in the manual. If you are happy with the results, you are good to go.

These technologies hold a lot of promise, but they are not perfect. YPAO, for example, tends to set most speakers to large and sets some distances incorrectly. YPAO users will often set speakers to small as they prefer the results of doing that. And they may manually correct distances.

Some people even prefer the sound after turning off the room correction features. Without a frequency analyzer system or software, it's hard to know what it's doing, so you may have to trust your ears and personal preference.

What is upconverting?

The answer depends on whether you are talking about DVD players, or AVRs. Upconverting DVD players can output video signals such as 720p, 1080i or even 1080p. That's the way manufacturers use the term for DVD players, and sometimes high definition players.

Upconverting AVRs can convert the video signal to a different type such as composite to component. The reason to consider an upconverting AVR is to be able to make a single connection from your AVR to your TV even though your video sources output different signals.

Upconverting is also known as transcoding.

Some scenarios may be helpful for understanding the process.

Let’s say that you have a game cube connected using its standard composite video cable. Your DVD player is connected with component video. With an AVR that does not upconvert, you would have to run a composite and a component video connection from the AVR to the TV. Depending on what you wanted to watch, you may have to switch inputs on both the AVR and the TV. With an AVR which can upconvert to component video, you can run a single component video connection to your TV.

In another scenario, say your AVR upconverts to HDMI. You have a VHS player connected (for your old Duke's of Hazard recordings,) a DVD player connected with component video, and your PS3 connected with HDMI. Turn on HDMI upconversion, and all your sources are converted to HDMI. You only need run a single HDMI cable to your TV. You can leave your TV input set to HDMI, and do your audio/video switching from your AVR.

Some TVs allow you to have different settings for each input. Using upconversion and switching from the AVR won’t allow you to use that ability on your TV, which is one downside to digitizing the signal, and there have been reports that on some AVRs with some sources, it has not worked correctly. For example, someone reported issues with HDMI upconversion of their old Nintendo game system.

Make sure you understand exactly what the upconversion feature on a given AVR offers, there are a number of variations.

What are deintelacing and upscaling?

Some AVRs have video processing capabilities. The three main abilities are –
• Upconverting from one video type to another (mentioned above)
• Deinterlacing signals
• Changing signals to a different resolution (scaling)

They may have other abilities as well such as noise reduction.

Before going into this topic, it should be noted that AVR video processors often have limitations which make them less useful. A common one, at the time this was written, is that many AVRs cannot deinterlace or scale HDMI signals, only analog. Even if an AVR can process HDMI, many players cannot output 480i over HDMI. They are stuck with 480p. Given that deinterlacing is arguably more important than scaling, that makes your video processor less useful. You may think, well then, I will just use component from my player to output 480i. But that forces a digital to analog conversion that HDMI avoided! You may think ok, I only want AVR video processing for cable/satellite, and I will connect a component video cable. And maybe it will help depending on exactly what your setup is. But you should understand the current limitations of the technology.

Scaling is fairly easy to understand. Video signals are made up of a series of frames. The frame consists of a series of pixels (picture elements.) We create a new frame with more pixels using information from existing pixels.

Deinterlacing involves assembling two fields into a video frame. Each field has half the lines of a video frame, either the even or the odd lines. The process isn’t trivial because the fields were captured at different points in time. For a good picture, a video processor needs to intelligently deal with that. DVD and high definition movies are usually stored at 24 frames per second, while video is commonly output at 30 frames per second. Deinterlacers need to deal with that mismatch (http://www.dvdfile.com/news/special_...2_pulldown.htm)

Deinterlacing is arguably harder than scaling. Which means that a good video processor in a AVR should be evaluated for its deinterlacer. DVD players are sometimes evaluated using a benchmark such as the Silicon Optix HQV benchmark. The same benchmark can be applied to an AVR. When reading a review on an AVR, take note of how they tested its video processing capabilities.

Most HDTVs have to deinterlace and scale signals which do not match their native resolution. The only exception would be CRT based HDTVs, which are uncommon. Most HDTVs have fixed pixel displays. LCD, Plasma and DLP display technologies are fixed pixel technologies. In fixed pixel displays, each video frame is made up of a fixed number of pixels. For example, a TV with a resolution of 1920x1080 has 1080 rows of 1920 pixels.

If you have a fixed pixel HDTV with a resolution of 1920x1080, it will convert all non 1080p signals to 1080p. Whether they be 480i analog from a cable box, 720p or 1080i they will be converted. Even 1080p inputs may not be exempt from scaling! (see the comments below on overscanning)

You should not consider video processing in a receiver because you think your 1080p TV is not giving you 1080p. It IS giving you that many pixels. The question is whether you can benefit from better deinterlacing and scaling in an AVR.

Turning on scaling may be undesirable. If your TV’s native resolution doesn’t match your setting, you will force multiple scaling to occur. For example, many LCD TVs have a resolution of 1376x768 which is called 720p, but isn’t really 720p. Older plasma TVs may have been advertised as 720p, but their resolution was not 1280x720. Scaling a DVD signal from 480 to 720 and sending that to a TV which does not have a true 720p resolution forces the TV to rescale the signal.

Another mismatch is with 1080p TVs. Even though most should have a true 1920x1080 resolution, they are likely set to to overscan the signal. This means that they crop the edges of the picture (http://en.wikipedia.org/wiki/Overscan.) This forces the TV to rescale regardless of what you send it. If you want to avoid this, you have to turn off overscan. If it won’t let you turn off overscan, your TV will always scale no matter what you send it. Even if you output 1080p from a blu-ray player, it will crop and rescan.

AVR video processors may do more than just deinterlace and scale. They may be able to perform tasks like video noise reduction. This can be good or bad. As video noise reduction is removing information, it could result in less detail.

The improvements of video processing can be subtle. Some videophiles have trained themselves to look for known issues, and therefore know what to look for. Untrained viewers may not even notice common deinterlacing issues. Don’t expect dramatic differences.

People looking for an AVR to improve a bad looking cable signal, shouldn’t expect much. Video processors can only do so much.

If you have multiple video processing options such as an upconverting video player and an AVR with upscaling capabilities, you may want to try out various combinations of settings to see which looks best (if any, you may not notice a difference.)

What equipment do I need for 3D Movies?

(This is based on my current understanding, this could change)

This section will discuss 3D movies on Blu-ray. These titles will use an extension to the AVC codec already support by Blu-ray players. It's expected most existing players won't be firmware upgradable.

The following hardware will likely be needed -

* Blu-ray player compatible with 3D titles
* Display compatible with 3D titles
* Glasses which compatible with 3D titles (These glasses work off a signal and will alternatively pass light for one eye and not the other using LCD technology)
* Optionally, An AVR which can pass the 3D signal

I have read that players will have multiple HDMI outputs so you can send the video separately from the audio if needed AVRs which won't pass the 3D signal; I have read current AVRs won't pass any 3D signal due to them not passing EDID information back to the player even if your display can support 3D and even if the bandwidth is supported by your AVR. So my present understanding is that you wont' need to replace your AVR, but if you want to retain full AV switching using your AVR, your would need to upgrade your AVR

If you have high speed HDMI cables, you will not need to upgrade your cables. If not, you may need to buy HDMI high speed cables. HDMI 1.4 does not increase bandwidth. The only change in cables for HDMI 1.4 is cables with ethernet support.

This was very informative, thanks for taking the time to put it together.

Yep. That was very informative. Mike, we appreciate your effort. For those who want to get into the nitty gritty details, it's an excellent and easy to understand FAQ. OTOH, most AVR's are in fact usable out of the box. The only requirement is that a user can identify all inputs and outputs, and can step through assignment of inputs if needed. For serious tweaking, the FAQ will be very helpful.

There are two key terms to understand when upscaling is discussed, deinterlacing and scaling.

When the television specification was created, the engineers chose to send only half the scan lines at a time (almost certainly due to broadcast bandwidth limitations.) We are stuck with that legacy, DVDs and cable use the same system. You may have seen the number 480i, which refers to standard definition interlaced video. For various reasons, we have moved to progressive scan displaying of interlaced signals. This requires assembling the even and odd fields of the interlaced signal into a single video frame. This sounds simple, but there are some issues involved. Because the two fields were scanned at slightly different times, moving images would be at slightly different positions on the even and odd scan lines. Another issue involves movies stored on DVDs at 24 frames per second being displayed at a higher frame rate (google 3:2 pulldown for the gory details.) Thus deinterlacing is non trivial.

Why all this talk of deinterlacing? AVRs usually have to include a deinterlacer as part of their video processing solution, and it's probaby a good idea to realize there's more to the process than simply adding more pixels.

Scaling is pretty simple to understand, the AVR simply adds pixels to a lower resolution signal to convert it to a higher resolution signal. For example from 640x480 (standard defintion TV) to 1280x780 (780p high defintion.) Note that this cannot add detail to the orignal image! It simply adds pixels, using information from existing pixels to create new ones (known as interpolation if you are mathematically inclined.) This looks just fine. To prove my point about not adding detail, goto into your photo editing program and keep zooming in until the image looks blurry. The photo program can't add detail missing from the photo and neither can your scaler. Which is why the term near HD quality when applied to scaling DVDs to higher resolutions may be a little misleading.

Understand this - all fixed pixel TVs and projectors have to deinterlace and scale signals which don't match their native resolution. Fixed pixel TVs include LCD, plasma and DLP based TVs whether they are projector based or flat screen models. Only CRT based TVs and projectors don't fall into that category. If you have a fixed pixel TV or projector, you don't need a deinterlacer/scaler in your DVD player or AVR to see the image in high defintion! All signals will be scaled to match the display's native resolution.

So why do you care whether your AVR has upscaling capabilities? Likely you don't. If your DVD player is good at upscaling, by all means use it's upscaler. Some people claim TVs usually have pretty good deinterlacing/scaling simply because that's what you are going to be seeing when looking at them in a store. In a store environment HDTVs are often fed with poor standard definition video signals. Manufacturers likely know this, and aren't going to totally skimp on an inferior solution.

Don't expect the AVR scaler to make a bad looking cable signal suddenly look like a DVD! And be at least somewhat suspicious of marketing buzz words like near high definition. They seem to be implying they can magically add missing detail - they can't!

If you have multiple options available, try them all out to see which works best.

Michael, excellent writeup - means a great deal to us that you contributed this! Thanks!

1 Question on Upscaling: when I connect the DVD via HDMI to the AVR can I still have the DVD do the processing or am I forced to let the AVR handle it?

You should be able to set any AVR with scaling to not scale the incoming signal. I believe I have it setup that way on my Yamaha RX-V2700. I can use upconversion (from component to HDMI in my case) while leaving scaling turned off.

I am a noob to all this and thinking of getting an Audio System for my livingroom.

Question about Upconverting/Upscaling.

Was thinking of getting either a onkyo 605 or 705 due to the good reviews and value.
Then read up that the Onkyo 875 and 905 can upconvert (maybe upscale) all sources to 1080p.
I think there are some other brands that does this but haven't checked them out yet.

So with the 875 or 905, it will change the output from AVR to TV to 1080p (maybe upscale) from all those sources? or I am not understanding it right?
Is this an important feature?
Will there be a noticeable PQ increase/decrease?

Trying to figure out if this upconverting/upscaling feature is soemthing I should invest in or not.
Or should I be happy getting the lower models?

I can only hazzard a guess. Switching usually means it cannot deal with audio. In this case, the suggestion seems to be that it handles 1.1 for audio, but can only switch 1.3. You would have to read the manual for the specifics.

FWIW - I have a 5.1 speaker setup, a 1080p plasma, comcast HD dvr, and a PS3.

Thanks!

I think repeater also means a signal boost. I know you can buy just an HDMI repeater which is placed in the HDMI signal path to "boost" the signal for long cable runs.

My Yamaha AVR does not mention "repeater" in the manual but I'm rather certain it "boosts" the HDMI signal. I had audio & video drops running a 50 foot HDMI cable from a STB Digital HD Tuner to my tv. When I fed that same tuner via HDMI to my AVR then HDMI out of AVR over the same 50 foot HDMI cable to tv, no more audio or video drops.

Have you considered adding some other common technical write ups regarding AVR issues & questions? Maybe get some others to contribute articles?

Things like:
- Do I really need HDMI 1.3
- How can I use the new HD Audio formats if my AVR does not decode HD Audio?
- What is the difference between player decoding and AVR decoding?
- Is there a difference between DSD vs MPCM? (SACD)
- Is there a difference between DD TrueHD / DTS HD vs MPCM?

And I'm sure a host of other issues that get quite confusing to consumers like ME. I don't know enough about these subjects to write such articles.

Added link to the Richard Clark challenge as an example of how hard it is to distinguish amplifier sound quality. I attempted to make that section more neutral, except for my final reccomendation which is clearly my opinion.

I have an Integra DPC-8.5 DVD universal player connected to an Arcam AVR300 receiver with a digital and 5 analog cables. I just purchased the HDAD of Alan Parson Eye in the Sky. On my receiver it is showing 24bit/96kHz sampling rate though I am playing the side which has 24/192. Is there anyway to play it at the higher sampling rate with this equipment setup? The DVD sounds great, I just want to see if I can hear it at the highest quality. Is this the correct forum for this question? Thanks in advance!

A comment about the Richard Clark challenge. In the early 70s I worked in a high end shop selling brands like McIntosh,Tandberg,Advent,AR,Thorens,Revox,Magnaplaner. ( I hope I remember how to spell them) One of the things we liked to do to mess with peoples minds is set up a test comparing the McIntosh power amp to the Dynaco ST-400. You will have to be pretty old to remember the Dynaco brand. I'm sure our test method was not nearly as sophisticated as Mr. Clark's. However, no one was able to reliably tell the difference played through a number of different speakers. Our favorite was the double Advent (stacked) playing a Duetsche Grammaphon disk on a Thorens turntable with a Shure SME tonearm. As good as it got at that point. We always called the Dynaco the poor mans McIntosh. The effect of expectations of the listener is immense. Our test method was far from perfect. Even though, we really couldn't tell the difference. It is my opinion that this is even more likely now with amp technology at the cost point it currently is. When I hear that someone is "blown away" by their new amp it makes me smile.

I am familar with Dynaco. They made one of the better selling stereo tube amps of all time. ST-70? I believe it was also available in kit form - and that the kit didn't require a lot of work to assemble?

A common claim is that you have to live with an amp for awhile before being able to decide if you like the sound. That would be a hard hypothesis to prove or disprove.

Anyway, if someone is already a great believe in amps sounding different they will simply discount my opinions in that section. I tried to stick keep that section bias free. My experience is that quality receivers all sound pretty good.

a few days ago, someone posted a link to a great reference chart that had quite a few receivers on it with a ton of info for comparison ... I have searched and searched and cannot seem to find it again ... I am mainly interested in seeing a list of receivers with three or more HDMI inputs ... many thanks to anyone that can post a link to that chart... I'll hang up and listen